Hitherto, liquid-phase based transfection system has been used for introduction of DNA into mammalian cells. The following methods have been used for transfection of mammalian cells so far.
(1) Calcium phosphate coprecipitation method (Chen, C. and Okayama, H.: Biotech., 6, 632-638, 1988),
(2) Lipofection-mediated transfer method (Rabindran S. K. et. al.: Science 259, 230-234, 1993),
(3) DEAE dextran-mediated transfer method (Sussman, D. J. and Milman, G.: Mol. Cell. Biol., 4, 1641-1643, 1984),
(4) Electroporation method (Chu, G. et. al.: Nuc. Acid. Res., 15, 1311-1326, 1987), and
(5) Microinjection method (Graessmann, M. and Graessmann A.: Proc. Natl. Acad. Sci. USA, 73, 366-370, 1976).
The above mentioned methods (1) to (4) need 104 to 106 cells as well as 0.1 to 10 μg DNA, in which the transfection efficiency is the maximal level of about 20%, although it is difficult to maintain the maximal transfection efficiency under various conditions. Especially, transfection efficiencies are variable depending on cell types and these transfection procedures are complicated and time-consuming. Under these circumstances, it is almost impossible to establish a high throughput transfection method by miniaturization and automation of the above mentioned transfection systems (1) to (4). In the meanwhile, the above mentioned method (5) requires much lesser amount of cells and DNA for transfection than the above mentioned methods (1) to (4), however, the procedure requires a high level of skill and a long-term experience since microinjection of DNA into cells is directly carried out under an observation with a microscope. Therefore, a liquid-phase transfection system is not suitable for high throughput transfection.
At present, a high throughput transfection system is highly required as shown in the following example: When cell proliferation is initiated by addition of various stimulations, the successive signal transductions are controlled by networks of interacting proteins.
Signal transduction and processing generally take place through specific protein-protein interactions mediated by protein structural transition and/or chemical transformations. Because of the complexity and our present incomplete understanding of protein circuitry and network dynamics and function, correlating a particular phenotype to a set of protein-protein interactions is not only a major undertaking but often requires methods that are amenable to genome-wide or targeted network analysis. The technology is highly required to analyze networks of interacting proteins encoded by the entire human genome. If high throughput transfection and monitoring systems are established, it is possible to express a target gene, to monitor the level of a gene product and to analyze the effect of the gene expression on cellular function in intact cells in real time.
The solid phase transfection technology is preferable to this purpose. In fact, J. Ziauddin and D. M. Sabatini have reported the solid phase-transfection method (Junaid Ziauddin & David M. Sabatini: Microarrays of cells expressing defined cDNAs, Nature 411, 107-110, 2001). In this paper, geratin is used to transfect DNA into cells by forming DNA-geratin complex to fuse with cell membrane. However, the method covers only a few cell lines, and has a problem for reproducibility and transfection efficiency.
Therefore, an object of the present invention is to provide a DNA array for high throughput solid-phase transfection, and a method for carrying out high throughput solid-phase transfection using the DNA array, which solve the above-mentioned problems.